The present invention relates to connectors used to attach coaxial cable to a mating port. Coaxial cable is widely used for the transmission of data. A common application is the transmission of television signals from a provider or source to an end user. A typical RG-6 or RG-59 coaxial cable comprises a central conductor surrounded by a dielectric insulator or core, which in turn is surrounded by a conductive shield. The shield is surrounded by a flexible, outer insulative jacket. The conductive shield may include one or more layers of a metallic foil and/or a braided metallic sleeve.
A free end of the coaxial cable is secured to a plug or port of a receiving unit by a coaxial cable connector. Releasable engagement elements are formed on the port and connector. In one typical arrangement the port has external threads that are engageable with internal threads on a nut of the connector. Other connectors use a bayonet type connection to the port. Different types of coaxial cable connectors are available and may be categorized by the manner in which they are secured to the cable. Screw-on type connectors are provided with an inner thread that cuts into the outer jacket of the cable when the connector is screwed onto the end of the cable. While such connectors are easily applied to a cable, many believe that they do not result in optimal signal transmission.
Radial crimp-type connectors include a metallic tubular portion that is placed over the end of the cable and subjected to a radial compression that deforms the tubular portion and causes it to grip the cable securely. Such a connector and an associated crimp tool are described in U.S. Pat. No. 5,138,864. A perceived inability of such connectors to provide a water-tight seal between the connector and cable has led to a decreased use of radial crimp-type connectors.
Axial compression-type connectors employ relative axial movement of two or more elements of the connector to secure the cable within the connector. Typically, such axial movement imparts a radial force that causes a portion of the connector to deform inwardly and grip the cable. For example, U.S. Pat. No. 6,089,913, which is hereby incorporated herein by reference, describes a coaxial cable connector with a crimping ring having a tapered inner surface. The crimping ring surrounds a thin metal sleeve that is coaxial with and spaced from an inner sleeve to form a jacket-receiving gap. The free end of a coaxial cable is pressed into the connector, typically with the central conductor, dielectric and foil layer entering the inner sleeve and the jacket and braided layer of the cable separating from the underlying dielectric insulator to occupy the jacket-receiving cavity between the inner and outer sleeves of the connector. With the cable so inserted in the connector, the crimping ring is advanced axially along the outer sleeve, which eventually causes the tapered inner surface of the crimping ring to bear against the outer sleeve. As the crimping ring continues to slide along the outer sleeve, it deforms the thin metal sleeve inwardly, thereby decreasing the gap between the sleeves of the connector and pinning the jacket and braided layer between the sleeves.
Another axial compression type connector is shown in U.S. Pat. No. 6,261,126, the disclosure of which is hereby incorporated herein by reference. In this connector the outer sleeve is not deformed during axial compression of a bushing. Instead, the bushing has a trailing end that has a reduced internal diameter that impinges on the cable jacket and pinches it between the bushing and the inner sleeve. A similar axial compression type connector is shown in U.S. Pat. No. 6,848,939, the disclosure of which is hereby incorporated herein by reference. It has an inner collar inside a bushing for engaging the jacket.
Regardless of the type of connector employed, a secure fit between the connector and the cable is important. An improperly fit connector-cable pair can become disengaged or provide an incomplete seal, which risks allowing moisture into the connector, thereby degrading the performance of the cable. Furthermore, the initial seating of the cable in the connector is important to assure a secure connection. Although tools are available for the purpose, the initial seating is typically done manually with the technician simply holding the connector in one hand and pressing the prepared cable end into the connector with the other hand. To make a proper connection the cable must advance fully into the connector but in some types of connectors the technician cannot see the interior of the connector to know where the cable is in relation to the connector.
It is also important that the connector seals against moisture entering the connector. While many connectors are installed indoors where moisture is not expected to be an issue, some will be installed in locations where moisture will definitely be a concern. Installers do not want to maintain inventories of “indoor” and “outdoor” connectors so one connector type must be suitable for both applications. In the past O-rings have been widely used to provide the necessary seals. While O-rings are generally effective, they do add cost and complexity to the connector. In some designs more than one O-ring is required to seal all the possible leakage paths. Press fitting parts of the connector together can also provide moisture seals but doing so adds to the complexity of the connector assembly process and the equipment needed in the factory.